Contact start/stop (CSS) mechanisms, load/unload mechanisms, and other mechanisms are found in disk drives as head mechanisms that cause a head/slider having at least one and typically two transducer heads to enter the data area on the disk or withdraw therefrom. The head mechanism does not intentionally let the head/slider touch the data area of the disk. A CSS mechanism causes the head/slider to withdraw to a landing zone on the disk before it touches the disk surface. A load/unload mechanism causes the head/slider to withdraw outside the disk, by moving the head arm that carries the head/slider onto a ramp provided near the inner diameter or outer diameter of the disk (thus unloading the head/slider), or causes the head/slider to move unloading the head/slider), or causes the head/slider to move onto the disk by moving the head arm from the ramp (thus loading the head/slider). A load/unload mechanism does not intentionally let the head/slider touch the disk surface. The operations of these types of head mechanisms are controlled by a head mechanism controller.
The data area surface of the disk of a CSS-type disk drive, and the disk surface of a load/unload-type disk drive, are smoothed; if the head/slider accidentally touches these smoothed surfaces, that is, if an accidental landing occurs, the disk surface may be damaged, or the head/slider may stick to the disk surface. In a load/unload-type of disk drive, there is a particularly high risk that the head/slider might stick due to an accidental landing, because the smoothness of the disk surface is heightened in order to heighten the data recording density by lowering the flying height of the head/slider from the disk surface. Some head mechanism controllers are provided with means for avoiding accidental landings.
As an example of a head mechanism controller provided with means for avoiding accidental landings, there is the head retract processor disclosed in Japanese Unexamined Patent Application 147463/1992. This head retract processor unloads the head/slider from the disk (causing it to withdraw from the data area) when it senses either vibration or a power supply drop.
In addition, the driving source signals such as clock signals to the driving circuit of the spindle motor that rotates the disk in a disk drive is controlled by a signal supply controller. Upon receiving one-bit data with a predetermined value from a higher-order controller, this signal supply controller stops the supply of driving source signals to the above driving circuit. The signal supply controller stops the supply of driving source signals when, for example, the disk drive is operated in a power-saving mode.
In the disk drives of the prior art described above, however, no measures were taken to avoid accidental landings due to abnormal operation of the spindle motor. In particular, if the head/slider was disposed over the disk (or over the data area) when the spindle motor stopped abnormally, an accidental landing was bound to occur. Abnormal stopping of the spindle motor might occur, for example, if one-bit data with the predetermined value was sent by mistake to the signal supply controller, due to a malfunction of the higher-order controller, stopping the supply of driving source signals even though the head/slider was disposed over the disk (or over the data area).
In a load/unload-type of disk drive, there is an additional risk that an accidental landing might occur if the head/slider is not loaded onto the disk at a predetermined velocity, so the head arm is driven with feedback control of the velocity of the actuator. Unloading also conforms to this driving method, except for power-off retract unloading when the power of the disk drive is switched off. If the disk drive receives a shock during loading or unloading with velocity control, however, the velocity of the actuator may depart greatly from the target value, and there is risk that an accidental landing might occur.